I remember the first time I played with YAML ten-ish years ago. I experimented with converting our configuration file from INI to YAML. It came with an actual noticeable increase to our app startup time in the tens of milliseconds.

The YAML evangelist in my company when asked told me I should cache the results… of reading our config file… from the local filesystem. What do I store that cache as? JSON? Just cut out the middle man. Left a really bad taste in my mouth at the time I have yet to get out.